1. Field of the Invention
The present invention relates to a semiconductor laser-pumped solid state laser system wherein an optical power from a semiconductor laser array as a pump source is optically coupled with a solid state laser element in high efficiency, and an optical coupling system for coupling an optical power from a semiconductor laser array with an optical fiber with high efficiency.
2. Description of the Related Art
A solid state laser using a semiconductor laser as a light source for optical pumping has attracted much attention because of its high efficiency, long life, and its potential miniaturization. Among the pumping methods of the solid state laser with the semiconductor laser, an end-pumping method wherein the solid state laser is pumped in the direction of its optical axis (e.g., Japanese Unexamined Patent Publication (Kokai) No. 58-528), realizes single fundamental transverse mode oscillation with high efficiency by matching the pump space of an optical power from the semiconductor laser with a spatial mode of the oscillation in the solid laser.
To obtain high output power from the semiconductor laser-pumped solid state laser, a light beam of the semiconductor laser must be sufficiently condensed and a semiconductor laser generating high optical power must be used.
Meanwhile, the optical power of a semiconductor laser, which is supplied through an optical fiber, has been widely used, for example, in the field of medical science. The optical power supplied through the optical fiber is obtained by optically coupling the semiconductor laser with the optical fiber. Again, to obtain high optical power from the optical fiber, the condensing of the optical power from the semiconductor laser and high output power from the semiconductor laser is important.
However, it is not easy to condense the optical power from the semiconductor laser because the divergence angle of the light beam of the semiconductor laser is large, and therefore, a condensing system must be located close to the semiconductor laser.
Furthermore, in the semiconductor laser, the laser beam is generated in a striped active layer, and since the optical power from a single striped laser is limited, a plurality of stripes having an array construction i.e., a semiconductor laser array has to be used to obtain the higher optical power.
Since the width of the semiconductor laser array generating an optical power sufficient for effecting the end-pumping amounts to 1 cm, a plurality of light beams cannot be condensed at a spot using a conventional lens system, and therefore the semiconductor laser array has not been employed in the end-pumping method efficiently, but has only been employed in a side-pumping method (for example, R. Burnham and A. D. Hays, Opt. Lett., 14, 27(1989); M. K. Reed, W. J. Kozlovsky, R. L. Byer, G. L. Harnagel, and P. S. Cross, Opt. Lett., 13. 204(1988).)